Suppose the marginal environmental damages per ton of CO₂equal $20 in tropical countries and $70 in temperate countries.There are 14 tropical countries and 40 temperate countries. All countries have marginal abatement cost for controlling CO₂is equal toMAC=50a, whereais the amount of abatement an individual country does.

How much CO₂will be abated in total around the world(the sum of all individual country's choices ofa)if countries cooperate to achieve the global optimum?